The telecommunication's industry had undergone tremendous growth and change since Alexander Graham Bell first invented the telephone in 1876. During the 20th century we have seen the introduction and evolution of a public wire line network that provides reliable and affordable voice and low speed data communications throughout the world. Until fairly recently, the telephone system utilized analog signals over hardwired land-lines for home and business communication. The installation of land lines is difficult and expensive especially in less developed areas of the world.
Mobile telephone communication was initially provided through a radiotelephone system. Each city had a single central tower with roughly 25 communication channels available to a small number of users with radiophones in cars. The central antenna had sufficient power to transmit about 50 miles. The system also required a high power antenna be instilled in each vehicle.
More recently, wireless telephone communication, cellular and cordless telephony, have gained wide spread popularity, but due to current limitations wireless phone service has not substantially displaced public wire-line networks. Despite the convenience and added flexibility of mobile cellular, most cell phone users continue to have land-line phone service at home and at the office with unique phone numbers that are different from their cell phone numbers. One reason users have not switched entirely to cellular is that the quality of cell phone service does not always match what they have grown accustomed to with the land-line service of the PSTN (Public Switched Telephone Network) or POTS (Plain Old Telephone System). Cell phone network coverage areas are often incomplete. There are dead zones in the network. Dead zones are small areas within a cell where signal strength in the cell phone providers network is weak or nonexistent High quality service everywhere in the network is not guaranteed.
The ultimate goal for wireless communication is to provide the end user with uninterrupted wireless communications capability anywhere without regard to location or mobility.
Both cellular and cordless telephony provide some degree of mobility for the end user. Cellular networks enables a cell phone, The mobile transceiver, to operate over a wide area throughout the network of cells. Cellular networks are designed to provide uninterrupted phone conversations to users traveling through the network by a hand-off of the call from one base station to another. The network is designed to attempt to provide seamless transfer of a call from one base station to another as the user crosses cell boundaries.
The basic cordless telephone proves a wireless alternative to the standard telephone. It utilizes a simple user installed base station that connects to a standard telephone interface of the PSTN to provide a limited range of mobility in a relatively small area. A single private cell is created in the vicinity of the base station typically 50 to 500 meters. Although there are some wireless PBX applications supporting cordless phones, most cordless phones are used in a very small area in the vicinity of a simple self installed base station connected to the PSTN.
Cell phone technology significantly increases the number of users that can simultaneously place wireless phone calls in the same geographic areas. Geographic region are divided into small cells allowing frequency reuse so that large numbers of people can simultaneously use their phones without interference. Cell phone networks can be complex configurations with smaller micro-cells existing within-larger macro cells. In a typical sample configuration each cell may be about 10 square miles. In general, all else being equal, as cell size decreases, the greater the frequency reuse, allowing much higher subscriber densities per MHz of spectrum. In other words, as cell size decreases system capacity increases.
Cell phone networks are comprised of individual cells that cover a specific geographic area within the network. Fixed position base station transceiver are used to create cells and the collection of cells constitute the network. It is a common mistake to believe that each cell has a centrally positioned transmitting tower and radio equipment known as a base station in the middle of the hexagon. Most cells are split into sectors to improve efficiency allowing them to carry more calls. Antennas normally transmit inward towards the center of each cell thus covering only a portion of each cell's geographic area, but not the whole cell. Each base station typically transmits and receives on 3 different sets of channels, one for each sector of the 3 cells it covers. Cells are commonly divided into 3 sectors, but sometime there are only 2 sectors and occasionally there are as may as 6. A cellular system will have coverage gaps and dead zones within cells, but the hexagonal shape makes it easier conceptually for the planner to visualize how the specific network is configured.
For simplicity, a cell is often conceptually thought of as a hexagon cell phone coverage grid created by a single base station transceiver. It is the geographic area in which a cell phone operates by communicating with a specific single base station. This is the definition of cell, what is meant, when the term is used hence forth in this document unless otherwise stated.
Base station installation necessary to create a cell site can be far easier and less expensive than land-line network installation; however, it requires preplanning and professional installation to ensure that adjacent cells in the network do not interfere with each other. The cellular network base stations typically have antenna that are positioned over 50 ft above the ground. These base stations are typically larger more permanent structures used to create standard cellphone network cells. Each cell typically has a coverage area radius of 0.5-30 km.
Thus a cell phone base station is a substantially fixed-permanent structure requiring substantial preplanning prior to installation. Operating frequencies must be selected to prevent interference with the preexisting cell networks in the area near where the base station will reside. Base station installation requires personnel with specialized skills to do the preplanning and install the base station. Even when temporary base stations are set up to handle unusually high call volumes in specific areas for things like sporting events, considerable preplanning work is required to set up and install these base stations.
A large number of these substantially fixed-permanent base stations, typically hundreds, are required in each geographic region to create a cell phone network. Each base station is connected to a Mobile Telephone Switching Office (MTSO). The MTSO controls all the base stations in the region and handles all the phone connections to other phone systems. The mobile cell phone and the base station transmissions within the cell do not propagate very far outside the cell because each has low power transmitters. Many cell phones have multiple signal strengths (e.g. 3 Watts and 0.6 Watts) to help reduce interference and conserve battery power.
Consider a common cell phone network configuration using a cluster of base stations with a frequency reuse pattern of 7 used to configure a provider network. It is a system where each cell uses one-seventh of the available communication channels to help ensure adjacent cells do not use the same frequencies to help prevent interference that would be caused when 2 cell phone users in close proximity attempt to place phone calls over the same channel. Each cell phone uses 2 frequencies per call in order to provide full duplex communication so that both parties can talk simultaneously. One frequency is used for the forward communication path, base station to mobile and the other provides the reverse path, mobile to base station communications. A Supervisory Audio Tone (SAT) is an inaudible high pitched tone that helps the system distinguish between callers on the same channel, but in different cells.
AMPS (Advanced Mobile Phone System) is a first generation analog cell phone system that has been available in the USA since 1983. An AMPS cell phone provider typically is allotted 832 frequencies to use in a city. 42 frequencies are used for cell phone control channels leaving 790 for voice communications. 2 frequencies are used for each voice channel leaving 395 voice channels per coverage area. Again a common configuration it to allocate one seventh of the available frequencies to each cell, which means that within any cell 56 people can talk at one time on  first generation analog cell phone system file AMPS. AMPS uses FM (frequency modulation) for voice transmission and FSK (frequency shift keying) for signaling. Each call uses a different frequency. This type of spectrum sharing is know as FDMA (frequency division multiple access).
Newer digital systems make better uses of the available channels enabling multiple simultaneous calls over voice channels. A digital cell phone system using TDMA (Time Division Multiple Access) can handle 168 simultaneous calls, 3 times the number that can be handled on an analog system. CDMA (Code Division Multiple Access) is a method for transmitting simultaneous signals over a shared portion of the spectrum. Qualcom for example operates CDMA cell phones in the 800 MHz band and 1.9 GHz PCS (Personal Communication Service) band. CDMA phones are noted for having excellent voice quality and long battery life. CDMA is less costly to implement, requiring fewer cell sites than GSM or TDMA digital cell phone systems and providing 3 to 5 times the calling capacity. CDMA is becoming widely used in North America and is also expected to become a 3rd generation technology for GSM (Global System for Mobile Communications). Currently GSM uses TDMA and is the predominant system in Europe and is also used around the world. Unlike GSM and TDMA, which divides the spectrum into different time slots. GSM defines the entire cellular system, not just the air interfaces (e.g. FDMA, TDMA, etc . . . ). CDMA uses a spread spectrum technique. A narrow band voice signal is spread across the full bandwidth of the CDMA channel. By using different codes, voice conversations share the full bandwidth. TDMA has a precise limit to the number of simultaneous calls it can support. CDMA has no hard limit. The quality of the call starts to diminish as additional users are added.
Roaming is a term used to describe a cell phone's ability to utilize another cell phone provider's network in order to place a call in an area without service by their provider. Roaming occurs when the subscriber of one wireless service users another providers wireless network. Roaming occurs if the System Identification Code (SID) on the control channel does not match the SID programmed into the user's cell phone. Roaming charges may be expensive especially since the second provider often has no direct preexisting financial contract with the user when the call is placed. In addition, the full complement of cell phone functions may not be available through another carriers network especially if it is an older analog network. If roaming is enabled on the cell phone and the carrier's signal becomes weak, roaming can occur even if it is a cell phone in operating in its' own home calling area. In addition, if the user's network provider is at full capacity in the cell, all 56 channels being utilized for example, the cell phone may be configured to roam, using another provider's network instead of having the call dropped or blocked.
Since cell phones rely on radio waves that travel through air, communication can at times be unreliable. Metal objects, weather conditions, large buildings, hilly terrain, and other objects can interrupt phone calls or prevent cell phone communication in specific areas of a cell all together. Antenna positioning and the surrounding landscape can create dead spots in a cell where signal strength is weak or non existent. This can be frustrating for customers especially when a dead zone coincides with their place of residence. The user may have a cell phone that works well most of the time, but when at home the cell phone may be non-operational or provide highly intermittent reception where many calls are dropped.
Furthermore, cell phone providers tend to concentrate on building cells and providing service in highly populated areas and areas well traveled. It is not uncommon to find no service outside of major cities or incur substantial additional roaming charges. This can be particularly frustrating for people with a favorite weekend retreat or the primary or second home away from the city. Users are often required to pay for a separate land-line with a different phone number in order to have phone service. A person attempting to reach someone may first call their cell phone number, then call their home number, then call their business number and finally try the number at their second home (assuming they know all these numbers). When the service is available call forwarding can be used to redirect phone cells from one number to another, but that requires repeated manual procedures to enable and disable.
There are systems available commercially that capture signals from an existing cell, transmit via wires into a building and then amplify and rebroadcast the signal within the building. These systems also capture the signal from cell phones within the building, transmit via wires to an antenna outside the building and them amplify the signals and rebroadcast. These systems can be used improve signal quality within a building in an existing cell. However, these systems do not extend the network outside the cell, but simply amplify existing cell phone signals within an existing cell. They require specialists to install and set up the equipment.
The Global Positioning System (GPS) was designed to allow users to determine their precise position anywhere on earth. It was originally designed for military navigation, but can now be used by anyone. With a relatively simple inexpensive receiver one's position anywhere on the earth can be determined at any moment. GPS consists of 27 earth-orbiting satellites, 24 in operation and 3 spares. Each satellite makes 2 complete rotations every day. The satellites are arranged so that at least 4 are visible in the sky at any location on earth at any time. The GPS receiver determines the distance to each satellite. With that information and using a mathematical principle called trilateration precise position can be determined. Regularly, at predetermined instants of time, the satellites begin transmitting a pseudo-random code. The receiver begins running the same digital pattern at the same time. By comparing the patterns from each satellite, it can determine the time lag which is then uses to determine the distance to each satellite. Only 3 satellites are required to determine one's position, but with the distance information from a 4th satellite the receiver can determine how far off its' quartz clock is from the extremely precise, but very expensive atomic clocks on each satellite and correct for any errors due to clocking variations. Thus, inexpensive quartz clocks can be used to reduce the cost of a GPS receiver and still provide extremely accurate positioning.
Caller ID can be used to transmit the phone number and sometimes the name of the caller to the phone receiving the call right after the first ring. A standard phone uses a 90 Volt AC 20 Hz ring signal. A technique known as FSK (Frequency Shift Keying) is used to transmit ASCII characters to the caller ID modem circuitry in-between the first and second ring